Background-Abnormal flow patterns in the left atrium in atrial fibrillation or mitral stenosis are associated with an increased risk of thrombosis and systemic embolisation; the characteristics of normal atrial flow that avoid stasis have not been well defined.Objectives-To present a three dimensional particle trace visualisation of normal left atrial flow in vivo, constructed from flow velocities in three dimensional space. Methods-Particle trace visualisation of time resolved three dimensional magnetic resonance imaging velocity measurements was used to provide a display of intracardiac flow without the limitations of angle sensitivity or restriction to imaging planes. Global flow patterns of the left atrium were studied in 11 healthy volunteers. Results-In all subjects vortical flow was observed in the atrium during systole and diastolic diastasis (mean (SD) duration of systolic vortex, 280 (77) ms; and of diastolic vortex, 256 (118) ms). The volume incorporated and recirculated within the vortices originated predominantly from the left pulmonary veins. Inflow from the right veins passed along the vortex periphery, constrained between the vortex and the atrial wall. Conclusions-Global left atrial flow in the normal human heart comprises consistent patterns specific to the phase of the cardiac cycle. Separate paths of left and right pulmonary venous inflow and vortex formation may have beneficial eVects in avoiding left atrial stasis in the normal subject in sinus rhythm. (Heart 2001;86:448-455)
Even though opinions differ as to whether lecturing is compatible with problem-based learning (PBL) or not, lectures are still a common form of instruction in PBL curricula. This paper discusses the lecture in the framework of theories of learning in general and the medical problem-based learning tradition in particular. An example of how theories of learning can be implemented in the lecture hall is presented. Theories that underpin PBL as an educational philosophy rather than as a method of instruction are reviewed. A lecture form, organized in introductory, in depth and application lectures, that responds to important factors for stimulating deep processing of knowledge and meaningful learning is discussed. Examples of and practical points about how to renew and restructure lectures in a way that counteracts surface approaches to learning, teacher centering and student passivity are presented. We argue that, with proper awareness of possible drawbacks of the large format, lectures can be used as valuable tools for learning also in a PBL curriculum.
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